The invention relates generally to prosthetic conduits or shunts used in surgery to bypass or reroute the flow of a bodily fluid. More particularly, the invention relates to conduits or shunts which are used temporarily during surgery to allow an uninterrupted flow of blood to tissues whose normal blood supply has been at least partially interrupted by a surgical procedure on a vessel such as an artery. These conduits are frequently used during procedures in which the affected tissue is particularly sensitive to a decreased blood supply. Examples of procedures in which sensitive tissues may benefit from an uninterrupted blood supply include carotid endarterectomy, coronary artery bypass grafting on an arrested, partially arrested or beating heart, and thoraco-abdominal aortic reconstructions. The use of a shunt during each of these procedures protects the brain, the myocardium, and the spinal cord, respectively.
Many different vascular shunts or catheters are currently employed during surgery to maintain blood flow in extremities and tissues served by a blood vessel undergoing a surgical procedure. One example, the Pruitt-Inahara carotid shunt (described in U.S. Pat. No. 3,435,824), includes the use of a tube having inflatable bladders encircling each end of the tube and further includes a duct for the passage of blood. During the surgical procedure, the vessel undergoing the procedure is partially cut through and the ends of the tube inserted into the vessel. The bladders are then inflated to a pressure that causes the ends of the tube to be retained within the vessel but without causing the vessel wall to overextend and rupture due to overinflation of the bladders. Care must be taken to monitor the pressure in the bladders during inflation to limit damage to the vessel though some damage to the endothelium is common. A central portion of the shunt between the ends remains outside the vessel and is commonly looped in a circular manner to prevent crimping of the plastic or silicone rubber tubing which forms the central portion of the shunt. Upon completion of the surgical procedure, the incisions around the ends of the shunt are loosely sutured, the bladders are deflated to permit the ends of the shunt to be withdrawn from the vessel, and the sutures are pulled tight to close the incisions.
Moses, U.S. Pat. No. 5,453,084, describes another example of a vascular shunt wherein a tube is inserted into the incised vessel and a ring clamp or purse suture is applied to the vessel wall at the position of each end of the tube to create a water seal between the vessel wall and the shunt tube and to hold the ends in place within the vessel. The tube is fabricated of a transparent material to permit observation of the fluid flowing through the shunt in order to verify that the shunt is functioning. In addition, the tubing material must be flexible enough to permit the tube to be manipulated into position but must also resist crimping so as not to occlude the flow of fluid through the shunt when it is bent. The shunt is removed by removing the ring clamps or loosening the purse sutures holding the shunt in place, withdrawing the shunt through the open incisions. The sutures are then tightened to close the incisions. The use of clamps or sutures to hold the shunt in place can cause neuro-muscular trauma to the vessel in the regions of contact.
Black, U.S. Pat. No. 5,129,883, describes a catheter adapted to be inserted into a patient""s circulatory system and threaded through to a portion of the system to be shunted. The catheter includes inflatable cuffs with a conduit that permits blood flow to bypass the region of the vessel between the cuffs. When the cuffs are inflated, blood flow is diverted through the conduit. As with the Pruitt-Inahara shunt above, the inflation pressure in the cuffs must be monitored to limit the amount of damage done to the vessel wall by the inflatable cuffs. Rayhanabad (U.S. Pat. No. 4,712,551) and Miller, Jr. et al. (U.S. Pat. No. 3,991,767) each describe variations on a tubular shunt with an inflatable cuff.
Healey, U.S. Pat. No. 4,721,109 describes a single piece device with a center tube and inflatable outer casing wherein the center tube fits into the ends of a damaged blood vessel to reconnect the two ends and conduct blood and the inflatable outer casing expands to secure the device within the vessel. Healey (U.S. Pat. No. 4,753,236) also describes a two piece device wherein each piece has an inflatable outer casing and a tubular internal portion wherein the two tubular portions include connectors adapted to couple to one another. The inflatable casings expand to secure each piece into an opening in a severed vessel and the tubular portions are coupled together to reconnect the ends of the vessel.
It is an object of the present invention to provide methods and devices for temporarily shunting a fluid-carrying vessel or tubular tissue structure in a living creature to provide uninterrupted flow of fluid through the vessel or tissue structure during a surgical procedure.
Another object of the present invention is to provide a shunt apparatus positionable within an incision in a blood vessel such that the shunt provides a substantially bloodless field around the incision site.
Another object of the present invention is to provide a shunt apparatus having a tubular structure constructed of an elastically deformable material that reduces circumferentially when axially lengthened and expands circumferentially toward an original, biased circumference when allowed to axially contract.
Another object of the present invention is that the circumference of the ends of the shunt apparatus will expand when the ends are released such that the ends securely lodge against the inner walls of a vessel into which the shunt is inserted and hold the shunt apparatus in place within the vessel lumen.
Yet another object of the present invention is that the circumference of the ends of the shunt apparatus may be reduced for easy insertion into the openings of an incised vessel.
It is a further object of the present invention that the shunt be secured within the vessel without the use of clamps or inflatable bladders.
It is an additional object of the present invention that the shunt apparatus may be easily repositioned within the vessel without interrupting the flow of fluid through the shunt apparatus.
Accordingly, the present invention provides a shunting device for implantation in a fluid-carrying vessel or tubular tissue structure having an elastically deformable, generally tubular body structure. The body structure has contiguous segments or regions including first and second end portions and a central region therebetween to collectively define a conduit having a longitudinal axis. Stretching at least one end portion of the shunting device along the longitudinal axis results in a reduction in a dimension of the tubular structure which is transverse to the longitudinal axis. The shunting device further includes means associated with the tubular body for facilitating the insertion and positioning of the shunting device within a vessel or tubular tissue structure. Such a means may include a receptacle integrally formed in the tubular body structure to receive a free-standing positioning stylus. Alternately, the means may include a stylus attached to one or both of the end portions of the tubular body with or without a positioning tube.
More particularly, the apparatus of the present invention includes a composite tube with a relatively large, relaxed circumference at both ends, and a smaller circumference section in the middle. The tube is constructed such that elongating the tube causes the circumference to reduce by about half. In a first embodiment, the tube is constructed of a tubular braided monofilament, which is then impregnated with an elastomeric material to provide vessel sealing and elasticity. Further, the larger circumference segments taper down to the smaller center segment, and the smaller circumference segment is substantially aligned with the outer aspect of the two larger circumference segments. Preferably, each of the ends of the tube is cut at an oblique angle.
Positioned on the outer surface along each the larger circumference segments of the tube is a closed-end positioning receptacle or cavity into which a stylus, such as a pushrod or wire, may be inserted to elongate the tube. This receptacle may extend partially along the larger circumference segment or back and over to the smaller circumference segment. The receptacle or cavity may be positioned on the outside surface of the main shunt tube, or it may be positioned along the inside surface of the tube at the ends and pass through the wall of the tube to the outer surface somewhere along the length of the tube. Ideally, this receptacle is sufficiently flexible that it collapses at least partially when the push rod is removed. This push rod receptacle may be fixed to the wall of the main shunt tube at the ends only or it may be fixed to the wall along the entire length. An advantage of extending the outer tube to the mid section of the shunt is that the shunt may be repositioned without removing the shunt from the vessel.
In another embodiment of the present invention, the shunt may have a thin stylus, such as a fine-gauge wire, attached to the tip of the obliquely cut end and extend back to at least the central portion of the shunt. The stylus may be used independently to stretch the shunt or may be used in conjunction with a narrow-lumen positioning sleeve, preferably made of metal or plastic. The position sleeve is passed over the wire to the end of the shunt while pulling on the wire to selectively extend the shunt. The pressure that the sleeve exerts against the end of the shunt causes elongation of the shunt which collapses the tube for easy insertion into a vessel.
In another embodiment, the wire stylus may have a sharpened distal end. In use, the sharpened end of the stylus is used to penetrate the outer surface of the end portion of the shunt. The stylus is then used to stretch the shunt so as to decrease the diameter of the shunt for insertion into the vessel. The shunt is preferably configured from a soft silicone or elastomer which allows penetration by the sharpened stylet without compromising the integrity of the blood lumen of the shunt.
In another embodiment of the present invention, a shunt positioning tool configured to securely hold and manipulate the shunt is provided. The positioning tool comprises a first and second elongate arm members which may be biased from an open to a closed position so as to securely engage a shunt between first and second semi-cylindrical distal ends of the arms. The shunt positioning tool may include a locking ring which is operable to securely fix the distal ends about the shunt during insertion or manipulation of the shunt. A pair of wire guides may also be included to accurately guide the distal movement of one or more stylets so as to stretch and contract the shunt for installation or manipulation of the shunt.
These and other objects, features and advantages will become apparent when considered with reference to the following description and the accompanying drawings.